As shown in FIG. 1, a prior art club head 10 has a striking face 12, a crown surface 14 and a sole surface 16. During a golf swing, the club head 10 is in an air flow stream 18. As is understood in aerodynamics, when air flows over a surface, such as a club head 10, forces near the surface 14 of the club head 10 create a velocity gradient from the surface 14, where air flow velocity may be relatively slow, to the free stream region 20, where air velocity is not influenced by the club head. This velocity gradient region is called the boundary layer. Flow separation occurs when the boundary layer travels on the golf club head 10 far enough against an adverse pressure gradient that the air flow velocity in the boundary layer relative to the surface of the club head almost falls to zero. The air flow becomes detached from the surface of the club head and takes the form of eddies and vorticies 22. Flow separation may result in increased drag which may be caused by the pressure differential between the front and rear surfaces of the club head. The increased drag may reduce the speed of the club head, which in turn may lower the velocity of a golf ball that is struck by the club head.
Generally golf club heads have had smooth exterior surfaces, with only grooves, i.e. scorelines, on the striking face of the club head. A smooth surface, however, may result in greater drag force on the club head, or increased separation of the air flow from the club head, and an associated reduction in club head speed.
U.S. Pat. No. 5,092,559 to Okumoto et al. illustrates a wood golf club head with steps extending transversely on an upper surface of the club head or a large dimple extending over the rear portion of the upper surface of the club head.
U.S. Pat. No. 6,001,029 to Kobayashi illustrates a club head with decreased air resistance having depressions formed on a back of a crown and side surfaces of a heel and toe of a club head. Each depression has a first side narrower than a second side thereof so that it is egg shaped. Gentle slopes are provided at the first side of each depression so that the generation of dead air region is suppressed at the inflow side of each depression and further decreases the air resistance in swinging.
U.S. Pat. No. 9,776,052 to Solheim et al. illustrates golf club head having a recess in the crown portion and a plurality of apertures is defined in the recess and a protective cover is configured to engage the crown to cover the plurality of the crown apertures.
U.S. Pat. No. 9,776,053 to Burnett et al. illustrates a golf club incorporating a trip step feature on the crown section. A portion of the trip step is located between a crown apex and the back of the club head and may be continuous or discontinuous.
U.S. Publ. No. 2017/0312591 to Saso illustrates a club head configured to decrease air resistance by avoiding the air flows from retouching the head surface. The club head is provided with a ridge structure which contains a first ridge and second ridge arranged at intervals in a downward direction of the air flows on at least the sole of a club head.
U.S. Publ. No. 2017/0319917 to Henrikson et al. illustrates a golf club with turbulators, including a plurality of ridges disposed on the crown of the club head and a method of manufacturing golf club heads with turbulators.
Thus, it is desirable to reduce the separation of the air flow from the club head so that associated drag on the club head is reduced thereby improving club head speed.